1. Field of the Invention
The present invention relates to the washing of bioassay plates generally and, more particularly, but not by way of limitation, to a novel washer for washing bioassay plates, the washer including concentric aspirate and wash needles.
2. Background Art
In clinical diagnostics and pharmaceutical research, a common protocol is enzyme linked immunosorbent assays (ELISA). In general terms, a reagent is bound to a container's surface. Other reagents react with the bound reagent, and are finally detected using an enzyme to cause a substrate to provide a color reaction. In these protocols, it is necessary to wash away the excess regent between each step.
The current de facto standard for ELISA protocols is to perform them in a 96-well microplate. Each well holds approximately 300 microliters. The wells are arranged on an 8.times.12 matrix on 9 mm centers. The antigen, or antibody, reagent is coated on the well surface. Typically, 200 microliters of a blocking reagent is added and allowed to react for a period of time with the antigen reagent. A plate washer is used to aspirate the blocking reagent from the well. Then, the well is refilled with a washing liquid and aspirated empty several times to remove any excess blocking reagent that is not bound to the side walls. This process is repeated several times with the other reagents used in the specific protocol.
Since the reaction is on the surface of the walls of the well and not in the liquid within the well, it is desirable to maximize the surface area and minimize the liquid reagents required to fill the well. This need for reduction in the use of reagents is driven by the cost of the reagents. Many antigens and antibodies must be grown in animals. This makes them precious.
To meet the demand for reduction in reagent use and cost and still meet the demands of high throughput screening, the trend is toward the use of a 384-well plate in the same overall physical dimensions as the current 96-well plate. The 384 wells are arranged in a 16.times.24 matrix on 4.5 mm center-to-center spacing. The brim volume of each well is approximately 80 microliters, with a working volume of around 30 microliters.
This close spacing obsoletes the plate washers that are currently on the market. The number of wells to be aspirated simultaneously increases four fold. This puts a different demand on the vacuum requirements for aspiration. The tight spacing requires a smaller, more precisely aligned wash and aspirate needle assembly.
For the foreseeable future, there will be a need to wash both 96-well and 384-well plates and to do so in a manner that washes all wells on a plate simultaneously. Heretofore, no plate washer has been known which could simultaneously wash all wells on a 384-well plate. Conventional washers for the latter type of plate employ two or three needles and treat one row of wells at a time.
Accordingly, it is a principal object of the present invention to provide a bioassay plate washer that can simultaneously wash all wells on a bioassay plate having a large number of wells.
It is a further object of the invention to provide such a bioassay plate washer that can easily accommodate bioassay plates having different numbers of wells.
It is an additional object of the invention to provide such a bioassay plate washer that is economically constructed.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.